JPH0348579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protected optical disc for recording information, and more particularly to an optical disc that retains information within a recording layer formed of a material sensitive to radiation. Regarding.

Disk structures for recording information by optical means usually have a layer that is sensitive to radiation and is formed on a rigid carrier. In order to prevent mechanical damage to the photosensitive layer due to external factors, the photosensitive layer is enclosed between two plates.

A first method of achieving this encapsulation is to provide a thick protective layer over the sensitive layer carried on the substrate, but this method has several drawbacks as described below. That is, a thick protective layer provided on the sensitive layer causes a decrease in the sensitivity of the sensitive layer to write radiation. Further, sublimated substances or decomposed substances generated by light irradiation cannot be removed from the sensitive layer. As a result, writing or recording performance is impaired.

A second way to achieve encapsulation is to form an encapsulation space in the form of an annular chamber above the sensitive layer. This space can be formed by a spacer or a cover-shaped element added to one or the other of the above-mentioned elements. This sealed space can be filled with neutral gas.

In the second method described above, if the air contained in the annular chamber is moist, there is a risk that the sensitive layer will be altered. That is, moisture can condense on the sensitive layer and have a detrimental effect on the sensitive layer. To prevent this, it has been proposed to place a protective layer of polymer or elastomer several tens of microns thick on the recording surface. Moisture that will deposit in the form of droplets on the top surface of this protective layer will be located at a distance from the focusing surface, so that it will have little influence on the light irradiation for reading or writing onto the sensitive layer. Therefore, it does not significantly affect the recording and reproducing operations of the disk.

Although such a solution is advantageous, however, the sensitivity of the sensitive layer still depends on the intensity of the light radiation due to the mechanical action of the protective layer facing the recording device.
The impact will reach up to 50%.

It is therefore an object of the present invention to provide a protected optical disc capable of reading and writing with high sensitivity without the risk of moisture condensation on the sensitive layer.

According to the present invention, the housing has an inner wall that defines a chamber, a surface that is exposed to the atmosphere inside the chamber, and is provided on a part of the inner wall to prevent light radiation from the outside. a sensitive layer that is sensitive to , and facing the sensitive layer such that it is exposed to moisture inside the chamber and does not come into contact with the sensitive layer in order to prevent moisture inside the chamber from condensing on said surface of the sensitive layer. This is achieved by means of a protected optical disc for recording information, comprising a hydrophilic coating provided on the other part of the inner wall.

According to the optical disk having the above configuration, the moisture inside the chamber is absorbed by the hydrophilic coating that is exposed to the moisture inside the chamber, and even when the temperature drops,
There is no condensation on the surfaces of the sensitive layer exposed to the atmosphere inside the chamber. The sensitive layer also has a surface that is exposed to the atmosphere inside the chamber, and reading or writing information on this surface does not impair the sensitivity of the sensitive layer.

Therefore, the optical disk having the above structure has no fear of condensation of moisture present in the chamber housing the sensitive layer on the sensitive layer, and enables highly sensitive reading and writing.

In the above configuration, it is desirable that the hydrophilic coating has a nucleus for the growth of water droplets on its surface, and it is also desirable that this hydrophilic coating is formed from an organic material. In this case, it is desirable that the organic substance is a polymer, and more preferably that the polymer is polyvinyl alcohol, polyvinyl acetate, or nitrocellulose. In addition, the housing
To prevent moisture from entering the room from outside,
Preferably, a moisture barrier layer is provided on the inner wall, excluding the area provided with the sensitive layer, and is substantially transparent to the optical radiation in the area traversed by the optical radiation. In this case, it is preferable that the moisture barrier layer is made of a material that is substantially unaffected by chemicals in the atmosphere, and particularly preferably of a metal. In this case, it is desirable that the metal be gold or a gold-based alloy. The moisture barrier layer may also be formed of an insulating amorphous amorphous glass, preferably a semiconductor glass, preferably an arsenic-based glass or Preferably it is a selenium-based glass. Further, it is preferable that the housing includes a member made of a material that is easily oxidized, and it is preferable that the easily oxidized material is a metal that is more electropositive than the metal that is included in the structure of the sensitive layer.

Embodiments of the invention will now be described in detail with reference to the accompanying drawings.

When information is reproduced by reflection,
One of the plates of the protected disk is made of an opaque, hard material that is impermeable to moisture. The other plate is necessarily transparent and is therefore generally made of plastic material. It is actually moisture permeable. If the substrate covered with the sensitive layer is made of plastic material, the ingress of moisture through the substrate occurs through pinholes necessarily present in the sensitive layer.

The moisture present in the annular chamber will condense on the photosensitive layer within a more or less long period of time if the temperature falls below the dew point. This moisture also acts as a catalyst for the oxidation of the photosensitive layer due to the oxygen present in the annular chamber. This causes mechanical stresses in the photosensitive layer during condensation and subsequent evaporation which would cause the layer to crack if it was very thin.

FIG. 1 is a cross-sectional view of one embodiment of a protected optical disk according to the present invention. This cross section was taken along one of the diameters of the disk. This disk includes a metal substrate 1. The metal substrate 1 is, for example, a rigid aluminum disk with a thickness of 1 to 3 mm, provided in the center with a hole 6 for inserting a drive shaft whose axis ZZ' coincides with the axis of the hole 6. The substrate 1 has been treated so that its inner surface, which forms the glossy layer, presents a satisfactory planar shape. The sensitive layer 3 is annularly provided on the substrate 1 and has an axis
An annular recording surface centered at ZZ' is formed. Fixed on the substrate is a circular cover 2 centered on the axis ZZ' and having a hole 7 drilled in its center having the same diameter as the hole 6. The substrate 1 and the cover 2 together form the housing of the optical disc. The fixing of the cover 2 onto the substrate 1 defines an annular chamber 5 above the recording surface. In this embodiment, the substrate is opaque and the recording or reproducing light 8 passes through the cover 2 to reach the recording surface, so this cover must be transparent to the light radiation. A portion of this light radiation will then be reflected by the sensitive layer. The cover 2 may be formed of a plastic material, for example polyvinyl chloride, and may also have a thickness of 1 mm.
It can have the following thickness: The cover 2 is adhered to the substrate 1 via the surface that is in contact with this substrate.
Moisture can therefore penetrate into the annular chamber through the permeable cover. To absorb this moisture,
A hydrophilic material is introduced into this annular chamber. Advantageously, this material is placed in direct contact with the cover. In FIG. 1, the cover is therefore coated on its inner surface with a hydrophilic coating 4 that is transparent to optical radiation. This coating can be formed from a hydrophilic polymer. Due to the presence of hydrophilic substances in the annular chamber 5, if the temperature drops below the dew point, there will be a change in the state of moisture present in the form of water vapor, starting from water nuclei that are absorbed on the surface of the hydrophilic material. It will have the appearance of small droplets of water.

The shape of the housing provided to the protected optical disk can be determined by the shape of the cover provided to the plate not carrying the sensitive layer, as shown in FIG.

Another embodiment of the housing, contrary to the previous example, is such that the plate carrying the sensitive layer is given the shape of a cover as shown in FIG.
This constitutes a variant of the protected optical disc according to the invention. This shape given to the rigid member 9, for example made of aluminum, delimits the annular chamber 12 that is enclosed when the plate member 10 covers this rigid member. As in the case of FIG. 1, the plate member 10 must be transparent for the recording or reproducing light 15 and may be made of plastic material. The members 9 and 10 each have the same diameter and the holes 14 and 1 of the same axis ZZ'.
3, the central part is bored out, allowing the passage of a drive shaft with axis ZZ'. A sensitive layer 11 is provided on the bottom annular surface of the member 9. In this example, the member 9 is opaque and the regeneration action takes place by reflection. The walls of the annular chamber 12 formed by the metal member 9 are impermeable to moisture. These walls therefore do not necessarily need to be covered with hydrophilic material. In this case, the hydrophilic substance, for example any polymer, need only cover the surface of the element 10 which serves to seal the chamber 12. Since this material is substantially hydrophilic, it does not necessarily cover the entire surface of the member. However, better efficiency would be ensured if all of the permeable walls were covered with hydrophilic material. As hydrophilic material polyvinyl alcohol, polyvinyl acetate or nitrocellulose can be used.

The method of combating moisture is to prevent moisture from penetrating through the permeable wall. For this purpose, all these walls can be covered with a material that acts as a barrier against moisture. An effective coating is formed by a metal layer with a selected thickness that is sufficiently small, at least in the areas where the recording or reproducing light is likely to pass, so that the passage of the light beam is not significantly impeded. This layer must have a thickness of at least 50 Å to be effective. The thickness may be any desired thickness in areas through which the light rays do not pass. In a preferred example, the metallic moisture barrier layer covering the area swept by the light beam is non-corrosive or the optical properties of this layer (translucency and reflectivity) are constant over time and read/write operations are prevented. It is chosen to be oxidized only to a very low degree so that it is not disturbed by oxidation of this layer. This coating can be produced by vapor deposition and can be formed by an alloy based on gold, silver, platinum or palladium, an alloy between these elements or any one of these elements. .

The moisture barrier material is amorphous and insulating and thus can be a non-rusting material, such as an amorphous semiconductor. For example, a 300 angstrom selenium-based glass coating can be used that provides a bandgap sufficient to prevent absorption of a significant amount of photons of the recording or reproducing light. Another possible material is an arsenic-based glass semiconductor.

FIG. 3 is a cross-sectional view of a modified protected plastic disc including a moisture barrier. The selected examples are read out by the transmission of light. It is therefore relevant for discs which require that the substrate carrying the photosensitive layer be transparent. However, the invention can also be applied to all other protected optical discs. FIG. 3 represents an optical disc with similar geometric characteristics to those of FIGS. 1 and 2. FIG.
This protected optical disc is in the form of a housing and a cap delimited by a substrate 17 and a member 18 delimiting the annular chamber 19.
have. This disc has two holes that allow the drive shaft to pass through.
It has an axis of symmetry ZZ' which is also the axis of 6 and 27. The substrate 17 is transparent, for example made of polyvinyl oxide approximately 1.5 mm thick, and further carries a sensitive layer 20 which can be written to and read by optical means. If layer 20 prevents moisture from entering chamber 19 through substrate 17, it is appropriate to protect other surfaces of the housing. cover 18
has a moisture barrier layer 23 extending on its inner surface in the area through which the readout beam 28 resulting from the incident beam 25 is modulated by the information contained in the sensitive layer 20.
covered with This barrier layer 23 is of the same type as previously described. The parts of the cover which are not subject to the passage of the readout beam are pre-covered with a layer of easily oxidizable material which allows the photosensitive layer to be protected from corrosion by oxygen. This oxidizable layer acts as an oxygen getter and can be selected to be as thick as necessary to further protect the sensitive layer during the required lifetime of the recording medium. This oxidizable layer can be formed by an organic layer, for example a red lead paint, containing metal particles or unsaturated metal oxides in suspension. In FIG. 3, this coating is applied to the area of the interior side surface left uncovered by the moisture barrier material.
It is applied to the two concentric rings 21 and 22.
The inner surface of this cover 18 is then covered with a hydrophilic material 24 of the same type as described above. This material is permeable to oxygen and therefore does not prevent oxygen from acting on materials susceptible to oxidation.

An advantage of the invention is that it can be applied to any type of protected optical disc having an annular chamber resting on the recording surface. In particular, the present invention is applicable to a protected optical disk having a sealing member in the form of a thin film as shown in FIG. The device includes a rigid member 29 made of aluminum, for example. This rigid member 29 is circular and made in the shape of a lid or dish. Its bottom has a flat surface that receives the sensitive layer 36. The member 29 has a central hole 31 with an axis ZZ' that coincides with the axis of the drive shaft.
has been opened. A flexible member 30 formed of a thin film of transparent plastic material is stretched loosely over edges 34 and 35 of rigid member 29. The upper surface of these edges forms the junction between members 29 and 30 arranged along two coplanar concentric rings with axis ZZ'. As shown in FIG. 4, the flexible member 30 can be bent towards the underside of the rigid member for better sealing for the annular chamber 33. If desired, the flexible member 30 is drilled with a central hole 32 to allow passage of the drive shaft. Membrane 30 is relatively permeable to moisture due to its thin dimensions (a few tenths of a millimeter at most) and the invention is therefore particularly desirable to be applied in this case. The inner surface of the member 30 is covered on its surface, which closes the annular chamber 33, with a layer 37 of a hydrophilic material transparent to the recording or reproducing light 40 of the type described above. The thickness of layer 37 is approximately 0.1 microns to 100 microns
It is micron. The interface between member 30 and layer 37 is formed by a layer 41 of moisture barrier material, such as a coating approximately 50 Å thick, deposited by evaporation. The rigid member 29 further carries a welded layer of easily oxidized material. For example, this layer consists of two concentric rings 38 and 39 centered on the axis ZZ'.
is generated in the form of These rings can be produced from a metal that is more electropositive than the metal used to form the sensitive layer, for example zinc or manganese, deposited by evaporation or electrochemical methods.

The presence of a hydrophilic layer ensures that there is no condensation on the sensitive layer. The presence of a moisture-impermeable coating was previously discussed. Experience has shown that only the presence of a moisture-impermeable coating can guarantee an unaltered shape for the housing of the disc when it is made of two parts made of hygroscopic material. was confirmed. Indeed, without this coating, only one part of the housing would be provided with a moisture barrier formed by the sensitive layer. As a result, saturation of this part occurs with a greater risk of contraction or expansion than the other part. In order for the two parts of the housing to be dimensionally equal, it is advantageous to have a part without a sensitive layer made of a very thin moisture-impermeable coating used as a moisture barrier. In this way, when atmospheric or temperature conditions change, the housing of the disk undergoes similar dimensional changes without any distortion of the surface carrying the sensitive layer. This coating is particularly useful when the housing member is made from polymethyl methacrylate.

The invention also applies to any type of protected optical disc in the form of a housing. It applies in particular to devices having an annular chamber formed by two panels in the form of flat disks separated by a concentric circular spacer.

The invention thus makes it possible to produce optical discs with a photosensitive layer that is protected from dust and abrasive damage, moisture and oxidation, and yet remains highly sensitive during reading and writing operations.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of a protected optical disc according to the invention, FIGS. 2 and 3 are sectional views of a variant of a protected optical disc according to the invention, and FIG. 4 is a thin seal. FIG. 2 is a cross-sectional view of a protected optical disc including a membrane. DESCRIPTION OF SYMBOLS 1... Metal substrate, 2... Circular cover, 3... Sensitive layer, 4... Hydrophilic substance coating, 5... Annular chamber,
7...hole.

Claims (1)

[Scope of Claims] 1. A housing having an inner wall that defines a chamber, and a surface that is exposed to the atmosphere inside the chamber, and is provided on a part of the inner wall to prevent light radiation from the outside. a sensitive layer that is sensitive, and a sensitive layer that is exposed to moisture inside the chamber and out of contact with the sensitive layer to prevent moisture inside the chamber from condensing on the surface of the sensitive layer; a hydrophilic coating on the other part of the inner wall opposite the layer. 2. An optical disc according to claim 1, wherein the hydrophilic coating has a nucleus for the growth of water droplets on its surface. 3. The optical disc according to claim 1 or 2, wherein the hydrophilic coating is formed from an organic material. 4. The optical disc according to claim 3, wherein the organic substance is a polymer. 5. The optical disc according to claim 4, wherein the polymer is polyvinyl alcohol. 6. The optical disc according to claim 4, wherein the polymer is polyvinyl acetate. 7. The optical disc according to claim 4, wherein the polymer is nitrocellulose. 8. The housing is provided on the inner wall except for a portion where the sensitive layer is provided, in order to prevent moisture from entering the room from the outside, and a portion traversed by the light radiation is substantially exposed to the light radiation. 8. An optical disc according to any one of claims 1 to 7, comprising a moisture barrier layer that is permeable to the optical disc. 9. The optical disc of claim 8, wherein the moisture barrier layer is formed of a material that is substantially unaffected by chemicals in the atmosphere. 10. The optical disc according to claim 8 or 9, wherein the moisture barrier layer is made of metal. 11 Claim 10, wherein the metal is gold
Optical disks as described in Section. 12. The optical disc according to claim 10, wherein the metal is a gold-based alloy. 13. The optical disk according to claim 8 or 9, wherein the moisture barrier layer is formed of insulating amorphous amorphous. 14. The optical disk of claim 13, wherein the amorphous is a semiconductor glass having a bandgap such that it does not substantially absorb optical radiation. 15. The optical disc according to claim 14, wherein the semiconductor glass is an arsenic-based glass. 16. The optical disc according to claim 15, wherein the semiconductor glass is a selenium-based glass. 17. The optical disc according to any one of claims 1 to 16, wherein the housing includes a member made of a material that is easily oxidized. 18. The optical disc according to claim 17, wherein the easily oxidized material is a metal that is more electropositive than the metals that participate in the composition of the sensitive layer.